[Bug libc/16625] New: sin gives wrong result with 2.19 on i386

["jtaylor.debian at googlemail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16625

            Bug ID: 16625
           Summary: sin gives wrong result with 2.19 on i386
           Product: glibc
           Version: 2.19
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: jtaylor.debian at googlemail dot com
                CC: drepper.fsp at gmail dot com

in ubuntu 14.04 i386 with glibc2.19 we are seeing wrong results for calls to
sin that don't appear with 2.18:
https://launchpadlibrarian.net/167193519/buildlog_ubuntu-trusty-i386.python-cffi_0.8.1-1ubuntu3_FAILEDTOBUILD.txt.gz


>       assert library.sin(12.3) == math.sin(12.3)
E       assert 0.8444952930965295 == -0.26323179136580094

I failed to create a testcase for as it seems to depend on global state.

to reproduce via the packages in 14.04 o

apt-get source python-cffi
cd python-cffi*
apt-get build-dep python-cffi
gdb --args python2.7 -m pytest testing/test_function.py
testing/test_zdistutils.py

from what I can tell with my limited assembly skills is that it computes the
right result but clobbers it in libc_feresetround_387_ctx

0xf7da2028 in libc_feresetround_387_ctx (ctx=0xffffa0a0) at
../sysdeps/i386/fpu/fenv_private.h:452
452      if (__glibc_unlikely (ctx->updated_status))
3: $st2 = 0.26251239976915330398554715429781936
2: $st1 = 7.2970669792260636173761756580191662e-08
1: $st0 = 0.84449529309652948683151407749392092


$st2 contains the right result, but its not returned to $st0 after the function
returns so cffi gets the wrong result.

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